Soybeans are considered one of the optimum sources for supplemental protein fed to livestock today. Raw soybeans, however, cannot be fed to livestock and consequently, raw soybeans must be treated in order to make them suitable feed supplements. The reason soybeans cannot be fed in the raw state is because proteolytic inhibiting substances are present in the raw soybeans. The presence of these inhibiting substances requires that the raw soybeans be cooked or heated in order to destroy the harmful urease enzymes and trypsin inhibitors. These substances in the raw soybeans have a retarding effect upon the growth of livestock and they can actually prevent proper utilization of the protein supplementation provided by the soybean feed material. Care must be taken in the heating process, however, because even though the heating is required to destroy the trypsin inhibitors, improper cooking will result in damage to the protein product itself.
In order to achieve a soybean feed product which is free of the inhibiting substances, most soybeans are now processed by a solvent-extraction method to produce what is commonly known as soybean meal. The solvent-extraction method, however, removes nearly all of the oil in the soybean so that the resultant soybean meal contains only about 0.5% of the original oil in the raw soybean.
In recent years, studies have been conducted to determine the caloric energy in oil or fat used to enhance livestock feed products. It has been proven that adding fat or oil to livestock feeding rations greatly enhances the efficiency of the feed. The drawback, however, is that actually adding animal or vegetable fat to the livestock diet is inconvenient and not always cost effective. One of the most convenient and economical ways of getting this added fat into the livestock diet is to provide soybeans which still contain the full oil or full-fat content of the bean. Each ton of full-fat soybeans contains approximately 360 pounds of oil.
As noted earlier, raw soybean cannot be fed to livestock because it contains inhibiting substances which have a retarding effect on the development and growth of monogastric animals. These undesirable proteolytic inhibitors, such as lipozidases and perioxidases, must be deactivated and removed from the soybean. Various processing methods have been developed for this removal of the inhibitors. These methods for processing differ considerably in their ability to provide full-fat soybean products, but all of the methods are consistent in the requirement of using heat to treat the raw soybean material.
One such method may be conveniently termed the "extrusion" method. In the extrusion method, full-fat soybean meal is prepared by an extrusion process in which heat and pressure are developed by passing the soybean by means of a screw extruder through the increasingly restricted extruder barrel. This confined movement of the soybean material causes heating of the soybean by attrition and pressure. The resulting product is discharged into the atmosphere where the sudden decrease in pressure results in expansion of the soybean material. Heating through the extruder acts to detoxify any anti-nutritive inhibiting substances. The expansion causes the oil cells within the soybean to rupture, and as the soybean product cools the oil is absorbed into the cells of the soybean. The processing temperature varies depending upon the moisture content of the soybean, as well as the maturity of the soybean. During the extrusion process, moisture is removed in the form of steam from the full-fat soybean and some of the undesirable urease activity properties are contained within the steam which is removed.
The extrusion method requires a substantial input of energy to operate the extrusion machinery, and the finished full-fat soybean product is not always consistent in urease activity, or protein or fat level since the processing temperatures vary depending on the moisture content and maturity of the starting raw soybeans. Furthermore, considerable expertise is involved in ensuring that the extrusion machinery runs properly, and there is a large soybean volume loss due to shrinkage of the soybeans. Since the oil cells are ruptured, the finished full-fat product is greasy and oily and, accordingly, the finished product is difficult to handle. The finished product does not flow freely through augers or other moving devices and because of the oil content, the shelf life is often reduced due to rancidity problems. This rancidity also causes the resultant soybean feed material to be less palatable to livestock.
A similar type of full-fat preparation process might be known as a modified extrusion soybean process. This technique also uses the concept of keeping the oil inside the finished soybean product. Raw soybeans are ground and subjected to a sulfite treatment and pH adjustment. Moisture content is standardized to 15% and the soybeans are extruded at 300.degree. F. This process results in thermal acceleration allowing greater production through the extruder while destruction of the proteolytic inhibitors takes place. This process, however, still has the drawbacks found in the previous extrusion process.
Another method for processing raw soybeans into a full-fat soybean protein source is the infrared roasting method, but there are great drawbacks to the use of infrared roasting on a commercial level. Due to the size of the equipment and the small quantity of raw soybeans that can be processed in a minimal length of time, infrared roasters are not normally used in commercial processing. The infrared process is more likely to be used by the individual feeder in a bulk or batch processing application directly at the feeding location.
In the infrared process, full-fat soybeans are prepared in an infrared roaster where the soybeans are heated by means of infrared roasting to deactivate the urease enzyme. When the soybeans are roasted there is considerable shrinkage and weight loss as a result of the decreased moisture content. The loss of moisture concentrates the nutrients to a certain degree, but if excessive heat is applied during the infrared processing, the feeding value may be greatly decreased because the protein content is undesirably affected by the excessive heat and some of the amino acids may become unavailable. In addition, further heat processing and/or physical processing may be necessary to achieve the maximum utilization of the energy of the fat in the roasted soybean. As found in the previously discussed methods, inconsistent protein values generated by the process make it difficult to maintain the feed ration values and insufficient urease activity removal retards growth efficiency in the livestock who are fed the infrared roasted soybeans.
By far, the most widely used method for treating soybeans is the solvent-extraction method which utilizes chemical extraction of the various inhibiting materials. The solvent-extraction process for processing soybean meal is totally different in concept than the previously discussed full-fat soybean treatment processes. The solvent-extraction method, however, does not have as its goal the preparation of a full-fat soybean product. In the solvent-extraction method, all but about 0.5% of the oil is removed. This leaves the remaining soybean meal with approximately 43% to 50% protein, approximately 1,350 kilocalories of metabolizable energy per pound and 2.7 to 3.5% lysine. The characteristics of the solvent-extraction method should be compared with the full-fat soybean which utilizes the whole soybean and contains approximately 38% protein, 1,650 kilocalories of metabolizable energy per pound and 2.4% lysine. The significant increases in these growth producing materials show the increased desirability of using full-fat soybean products.
These prior art methods, while having the common goal of obtaining a full-fat soybean livestock feed product, have common drawbacks and problems. Of primary concern is overcooking or undercooking of the soybean. It is difficult to regulate the quality of the feed product when it is difficult to regulate the cooking of the soybean. Consequently, one of the major problems is consistency of the product.
While it is known that heat processing and/or physical processing is necessary to obtain the maximum utilization of the energy-fat in the soybean, if excessive heat is applied during the processing, the feeding value may be low because some of the amino acids will become unavailable for use in the feed product. If raw soybean is taken through any of these treating processes and left undercooked, that is, not enough heat is applied, urease activity will be high and the the trypsin inhibitors will not be destroyed.
When soybeans are treated in either the extrusion or roasting process, there is also considerable shrinkage or weight loss due to the loss of moisture. This can be a problem since the feed buyer normally pays for the weight loss and weight loss increases the price of the finished product. For example, if 1,000 pounds of soybeans are processed and there is a 5% weight loss due to moisture loss, only 950 pounds of processed soybeans will be obtained.
An additional problem which is common to the extruded soybean product is spoilage in the finished full-fat product. The oil cells of the soybean are ruptured during processing so that the end product is "greasy" and oil-filled. This release of oil has a tendency to increase rancidity and spoilage. The shelf life of the full-fat extruded soybean is also decreased because of the ruptured oil cells.
These products also have a tendency to bridge so that flowability of the finished product is a definite problem. Energy consumption is another consideration with these prior processes, since it requires a considerable amount of energy to run extruders and roasters. Also required are experienced laborers who must be well trained to adapt and modify the equipment according to moisture levels in the raw soybeans. Finally, the consistency of the urease activity (the measure by which the elimination of the trypsin in integers is measured) is not good in the prior methods.